Video Transcript
Which of the following is not a property of metals that result from metallic bonding? (A) Good conduction of heat, (B) good conduction of electricity, (C) low density, (D) high melting and boiling points, (E) malleability and ductility.
In this question, we want to determine which option is not a property of metallically bonded lattice. So first let’s investigate what metallic bonding is.
Metals form as the valence electrons of metal atoms effectively decouple from parent metal atoms. The metal atoms turn into positively charged ions as their valence electrons group and make one sea of electrons. We say these electrons are delocalized, since they are free of their parent atoms. A metallic bond is a strong electrostatic force of attraction between positively charged ions and negatively charged delocalized valence electrons.
Metals have characteristic properties because of these forces of attraction between their metal cations and their sea of delocalized electrons. Metals tend to have high melting and boiling points because of metallic bonding forces. It takes a lot of thermal energy to overcome the forces of attraction between the metal cations and delocalized electrons and to change their physical state. Almost all pure metals are solid at room temperature, but mercury is a notable exception. We can rule out answer option (D), high melting and boiling points, as this is a property of metals and we are asked to find which is not a property of metals.
The delocalized electrons in metals are highly mobile and can move from the negative terminal of an electric circuit to its positive terminal. And so metals tend to be good conductors of electricity. And so we can see that answer (B), good conduction of electricity, is not an answer.
Metals also tend to be good conductors of thermal energy. The cations vibrate and transfer thermal energy relatively slowly, while the delocalized electrons transfer heat energy faster as they move rapidly between the metal cations. We can rule out answer option (A), good conduction of heat, because this is a property of metals.
Strong metallic bonds result in dense packing in metals. The cations are held close together because of the sea of delocalized electrons. So when pulled or hammered, the sea of delocalized electrons changes shape as one layer of cations slides over another. And this is why metals are malleable and ductile. And so we can rule out answer option (E), malleability and ductility.
We are left with answer option (C), low density. And this makes sense. We have seen that the cations in metals are densely packed. And indeed, metals in general do have high density.
So which of the following is not a property of metals that result from metallic bonding? The answer is (C) low density.
